System and Method for Communications Link Control

ABSTRACT

A method for operating an access point includes identifying one or more stations to receive a transmission from the access point, and generating a traffic indication map (TIM) for the one or more stations identified, the TIM in accordance with a TIM generating rule, the TIM identifying at least an offset length and a number of entries. The method further includes broadcasting a beacon carrying the TIM to the one or more stations identified, the one or more stations configured to decode the beacon according to the TIM generating rule.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. application Ser. No.13/681,093, filed on Nov. 19, 2012, entitled “System and Method forCommunication Link Control,” which claims the benefit of U.S.Provisional Application No. 61/561,707, filed on Nov. 18, 2011, entitled“System and Method for Downlink and Uplink Control in WiFi Networks,”which applications are hereby incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates generally to digital communications, andmore particularly to a system and method for communications linkcontrol.

BACKGROUND

In an IEEE 802.11 compliant communications system (also known as WiFi),an access point (AP) serves one or more stations (STA) by receivingtransmissions from the one or more STA and forwarding the transmissionsto their intended destinations. Similarly, the AP receives atransmission intended for one of its STA and forwards the transmissionto the STA. A transmission occurs over unidirectional channels referredto as communications links. A transmission from a STA to the AP may bereferred as an uplink (UL) transmission, while a transmission from theAP to a STA may be referred to as a downlink (DL) transmission.

FIG. 1 illustrates a portion of a prior art beacon 100. Beacon 100 istransmitted periodically by an AP and includes an element identifier(element ID) field 105, a length field 110, a delivery trafficindication map (DTIM) count field 115, a DTIM period field 120, a bitmapcontrol field 125, and a partial virtual bitmap field 130. Element IDfield 105, length field 110, DTIM count field 115, DTIM period field120, and bitmap control field 125 contain information identifying andspecifying a traffic indication map (TIM) bitmap contained in partialvirtual bitmap field 130. The TIM bitmap is maintained by the AP or amesh STA and consists of up to 2008 bits organized into 251 octets. AnN-th bit (0≦N≦2007) in the TIM bitmap corresponds to bit number (N mod8) in octet [N/8] where a low-order bit of each octet is bit number 0and a high-order bit of each octet is bit number 7. Each bit in the TIMbitmap corresponds to traffic (data) buffered for a specific STA in abasic service set (BSS) that the AP is going to transmit at a time thatbeacon 100 is transmitted or a specific neighbor peer mesh STA withinthe mesh BSS (MBSS) that the mesh STA is going to transmit at a timethat beacon 100 is transmitted.

The N-th bit in the TIM bitmap is set to “o” if there is no data (e.g.,individually addressed MAC service data unit (MSDU) and/or MACmanagement protocol data unit (MMPDU)) for the STA corresponding to theN-th bit. If there are any individually addressed data, e.g., MSDUand/or MMPDU, for the STA corresponding to the N-th bit, then the N-thbit in the TIM bitmap is set to “1”. It is noted that in legacy IEEE802.11 systems, e.g., those that are compliant to IEEE 802.11 a, 802.11g, 802.11 n, 802.11 ac, and the like, the maximum number of STAs in aBSS is 2007, so the TIM bitmap is capable of representing all STAs of asingle BSS.

SUMMARY

Example embodiments of the present disclosure which provide a system andmethod for communications link control.

In accordance with an example embodiment of the present disclosure, amethod for operating an access point is provided. The method includesidentifying, by the access point, one or more stations to receive afirst transmission from the access point. The method also includesgenerating, by the access point, a traffic indication map (TIM) for theone or more stations identified in the TIM in accordance with a TIMgenerating rule, the TIM identifying at least an offset length and anumber of entries. The method further includes broadcasting, by theaccess point, a beacon carrying the TIM to the one or more stationsidentified, the one or more stations configured to decode the beaconaccording to the TIM generating rule.

In accordance with another example embodiment of the present disclosure,a method for operating a station is provided. The method includesreceiving, by the station, a first beacon including a traffic indicationmap (TIM) from an access point, and identifying, by the station, one ormore stations to receive a first transmission from the access point fromthe TIM in accordance with a TIM generating rule identifying at least anoffset length and a number of entries. The method also includesdetermining, by the station, if the station is one of the one or morestations identified, and receiving, by the station, a secondtransmission from the access point if the station is one of the one ormore stations identified.

In accordance with another example embodiment of the present disclosure,an access point is provided. The access point includes a processor, anda transmitter operatively coupled to the processor. The processoridentifies one or more stations to receive a first transmission from theaccess point, and generates a traffic indication map (TIM) for the oneor more stations identified, the TIM in accordance with a TIM generatingrule identifying at least an offset length and a number of entries. Thetransmitter broadcasts a beacon carrying the TIM to the one or morestations identified, the one or more stations configured to decode thebeacon according to the TIM generating rule.

One advantage of an embodiment is that stations that do not receive anyor very little traffic may not need to monitor for an indicator of suchtraffic, therefore, the stations may be able to sleep for extendedperiods of time. Hence, the power consumption of the stations may bereduced and the battery life of the stations may be increased.

A further advantage of an embodiment is that efficient techniques forTIM signaling are provided to help reduce TIM signaling overhead, whichhelps improve overall communications system performance.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawing, in which:

FIG. 1 illustrates a portion of a prior art beacon;

FIG. 2a illustrates an example communications system according toexample embodiments described herein;

FIG. 2b illustrates an example communications system, wherein thecommunications system includes sensor devices and traffic offloadingdevices

FIG. 3a illustrates an example diagram of an AID address space with ahard separation according to example embodiments described herein;

FIG. 3b illustrates an example diagram of an AID address space with asoft separation according to example embodiments described herein;

FIG. 4 illustrates an example TIM station's AID according to exampleembodiments described herein;

FIG. 5 illustrates an example non-TIM station's AID according to exampleembodiments described herein;

FIG. 6a illustrates an example TIM that indicates stations receiving atransmission by an AP, the TIM is generated according to a first TIMgeneration rule according to example embodiments described herein;

FIG. 6b illustrates an example TIM that indicates stations receiving atransmission by an AP, the TIM is generated according to a modificationof the first TIM generation rule according to example embodimentsdescribed herein;

FIG. 6c illustrates an example TIM that indicates stations receiving atransmission by an AP, the TIM is generated according to a second TIMgeneration rule according to example embodiments described herein;

FIG. 6d illustrates an example TIM that indicates stations receiving atransmission by an AP, the TIM is generated according to a third TIMgeneration rule according to example embodiments described herein;

FIG. 7a illustrates an example flow diagram of operations in an AP asthe AP transmits to stations according to example embodiments describedherein;

FIG. 7b illustrates an example flow diagram of operations in a stationas the station receives a transmission from an AP according to exampleembodiments described herein;

FIGS. 8a through 8c illustrate example beacons for supporting multiplestation types according to example embodiments described herein;

FIG. 9a illustrates an example flow diagram of operations in an APgenerating a beacon according to example embodiments described herein;

FIG. 9b illustrates an example flow diagram of operations in a TIMstation receiving a beacon according to example embodiments describedherein;

FIG. 9c illustrates an example flow diagram of operations in a non-TIMstation receiving a beacon according to example embodiments describedherein;

FIG. 10 illustrates an example first communications device according toexample embodiments described herein; and

FIG. 11 illustrates an example second communications device according toexample embodiments described herein.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The operating of the current example embodiments and the structurethereof are discussed in detail below. It should be appreciated,however, that the present disclosure provides many applicable inventiveconcepts that can be embodied in a wide variety of specific contexts.The specific embodiments discussed are merely illustrative of specificstructures of the disclosure and ways to operate the disclosure, and donot limit the scope of the disclosure.

One embodiment of the disclosure relates to communications link control.For example, at an access point, the access point identifies one or morestations to receive a transmission from the access point, and generatesa traffic indication map (TIM) for the one or more stations identifiedin the TIM in accordance with a TIM generating rule identifying at leastan offset length and a number of entries. The access point alsobroadcasts a beacon carrying the TIM to the one or more stationsidentified, the one or more stations configured to decode the beaconaccording to the TIM generating rule. As another example, at a station,the station receives a beacon including a traffic indication map (TIM)from an access point, and identifies one or more stations to receive atransmission from the access point from the TIM in accordance with a TIMgenerating rule identifying at least an offset length and a number ofentries. The station also determines if the station is one of the one ormore stations identified, and receives a transmission from the accesspoint if the station is one of the one or more stations identified.

The present disclosure will be described with respect to exampleembodiments in a specific context, namely downlink data transmissions inan IEEE 802.11 compliant communications system. The disclosure may alsobe applied, however, to uplink data transmissions in an IEEE 802.11compliant communications systems, as well as uplink and/or downlink datatransmissions in other standards compliant communications systems andnon-standards compliant communications systems wherein an indicator oftransmissions are presented to communications devices.

FIG. 2a illustrates a communications system 200. Communications system200 includes an AP 205 that serves a plurality of stations, such asstation 210, station 212, station 214, and station 216. AP 205periodically transmits a beacon that includes a TIM bitmap to indicatewhich station AP 205 has buffered data for. The plurality of stationslisten to the beacon, which includes detecting and decoding the beacon,and determines if it will be receiving a transmission from AP 205. If astation will be receiving a transmission from AP 205, then the stationmay remain awake to receive the transmission. If a station will not bereceiving a transmission from AP 205, then the station may go to sleepor perform some other operation.

Recently, a new task group, TGah, has been formed to preparespecifications for under 1 GHz WiFi. The 1 GHz WiFi as specified by TGahis mainly targeted towards sensor networks with traffic offloading fromcellular networks being a secondary usage scenario. A requirement forthe specifications is to support more than 6000 stations. The 1 GHz WiFiwill operate in a narrow bandwidth (between 1 and 2 MHz) achieved bydownclocking 20 MHz WiFi implementations. However, this naturally leadsto an increased length in the symbol duration from 4 us in 20 MHz to 40us in 2 MHz.

FIG. 2b illustrates a communications system 250, wherein communicationssystem 250 includes sensor devices and traffic offloading devices.Communications system 250 may be compliant to the 1 GHz WiFi asspecified by TGah. Communications system 250 includes an AP 255 servinga plurality of sensor devices, such as sensor 260 and sensor 262, aswell as a plurality of traffic offloading devices, such as offloaddevice 265 and offload device 267. AP 255 may periodically transmit abeacon including a TIM bitmap to indicate to the devices served by AP255, e.g., the sensor devices and the traffic offloading devices, aswell as other types of devices, which of them AP 255 will betransmitting downlink data to. It is noted that communications system250 may also include other communications devices, such as computers,tablets, telephones, printers, televisions, relays, and the like.However, for simplicity reasons, communications system 250 is shown asincluding one AP, five sensor devices, and three offload devices.

However, sensor devices generally make their measurements and transmitthe measurements to an information aggregator via AP 255 and typicallydo not receive any or very little downlink data. In other words, sensordevices predominantly make UL transmissions while receiving very few orno DL transmissions. Hence, for a majority of the time, bits in the TIMbitmap corresponding to the sensor devices may likely be set to “o” orwithout downlink data.

Traffic offloading devices, as well as other devices, such as userequipment (UE), smart phones, computers, tablets, and the like,predominantly receive DL transmissions while typically making a smallernumber of UL transmissions. Therefore, there is high probability thatbits in the TIM bitmap corresponding to offloading devices will be setto “1” or with downlink data.

Additionally, since sensor devices are usually battery powered, powerconsumption is another important consideration in sensor networks. Anyadditional overhead, such as communications overhead, would lead to ashorter battery life, which implies additional costs involved in batteryreplacement. As an example, if a TIM bitmap was used in the 1 GHz WiFias specified by TGah, the TIM bitmap would be at least 6000 bits long(with 1 bit per station) and a beacon including the TIM bitmap would belonger than 40 ms long. A sensor actively receiving a 40 ms transmissionwould consume a large amount of energy, thereby significantly shorteningits battery life. Therefore, it may be desirable to not require sensordevices, as well as other devices that have very little or no downlinkdata, to detect and decode the TIM bitmap, which can result in asignificant reduction in power consumption. The sensor devices may becharacterized by low duty cycle traffic. Between transmissions they mayconserve the energy by switching to a sleep or suspend mode. Sensordevices wake up for UL transmissions.

It is noted that although the discussion focuses on downlink data andTIM bitmaps for downlink transmissions, the example embodimentspresented herein are also operable for uplink data and TIM bitmaps foruplink transmissions. Therefore, the discussion of downlink data and TIMbitmaps for downlink transmissions should not be construed as beinglimiting to either the scope or the spirit of the example embodiments.

According to an example embodiment, stations in a communications systemmay be categorized into one of two types according to their TIM status,i.e., their use or non-use of the TIM bitmap for downlink data and/oruplink data signaling. A first station type may be referred to as a TIMstation (or simply TIM-needed station), which includes stations thatmake use of the TIM bitmap for downlink data and/or uplink datasignaling. Examples of TIM stations may include traffic offloadingdevices, UEs, computers, tablets, and the like. A second station typemay be referred to as a non-TIM station (or simply TIM-unneededstation), which includes stations that do not use the TIM bitmap fordownlink data and/or uplink data signaling. Examples of non-TIM devicesinclude sensor devices, as well as other devices that have little or nodownlink data and/or uplink data. Tables 1 and 2 present summaries ofstation types for downlink data and uplink data signaling where an Xrepresents a situation where any value is ok.

TABLE 1 Summary of Station Types for Downlink Data Signaling StationType Uplink Data Downlink Data TIM YES YES Non-TIM X NO/Little

As shown in Table 1, a station may be classified as a non-TIM stationwhen it has little or no downlink data. Additionally, a station may beclassified as non-TIM station if its downlink data can tolerate arelatively large delay and therefore it can be requested by the stationfrom the AP at arbitrary time.

Since there are a number of types of stations, e.g., TIM and non-TIM, aseparation in AID address space for the different types of stations maybe beneficial. Separation of the AID address space may simplifyidentification and AID allocation for a station. As an example, if astation has an AID location in a particular region of the AID addressspace, the station's type is readily known. It is noted that thediscussion presented below focuses on separating the AID address spaceinto two regions. However, the AID address space may be separated intoany number of regions to meet the number of types of stations.

According to an example embodiment, the separation of the AID addressspace may be a hard separation wherein predefined numbers of AIDs arereserved for different types of stations. In other words, a certainnumber of AIDs are reserved for the TIM devices. The number can bepre-defined, or by negotiation, or determined by the AP and broadcast tothe BSS via beacon or some other messages. As an example, the number ofAIDs reserved for TIM devices may be fixed. With the number of AIDsfixed, the size of the TIM may also be fixed. FIG. 3a illustrates adiagram of an AID address space 300 with a hard separation. As shown inFIG. 3a , AID address space 300 is separated into a TIM AIDs space 305and a non-TIM AIDs space 310. AIDs for stations may be taken from anappropriate AIDs space depending on the type of the station. It is notedthat since the separation is a hard separation, the number of AIDsavailable per type of station is fixed.

According to another example embodiment, the separation of the AIDaddress space may be a soft separation where AIDs for a first type ofstation may begin at a first specified part of the AID address space,while AIDs for a second type of station may begin at a second specifiedpart of the AID address space. As an example, AIDs for non-TIM stationsare allocated from the high address place of the AID space and the AIDsfor TIM stations are allocated from the low address place of the AIDaddress space. With the number of AIDs potentially being variable, thesize of the representation of the TIM may also be variable. FIG. 3billustrates a diagram of an AID address space 350 with a softseparation. As shown in FIG. 3b , AID address space 350 includes a TIMAIDs space 355 and a non-TIM AIDs space 360. AID address space alsoincludes an unassigned region 365 that includes AIDs that may beassigned to either TIM stations or non-TIM stations. As AIDs areassigned, the respective AIDs space grows. As an example, as AIDs areassigned to TIM stations, TIM AIDs space 355 grows to the right, whileas AIDs are assigned to non-TIM stations, non-TIM AIDs space 360 growsto the left. It is noted that since the separation is a soft separation,the number of AIDs available for a particular type of station is limitedonly by a total AID address space and a number of the other types ofstations.

According to another example embodiment, AID allocation for TIM andnon-TIM stations may use different AID address definitions. In order todistinguish them from some other messages that also use AIDs to identifystations, there may be a specific value, e.g., a sequence of bits, inthe AID. As an example, both types of stations' AIDs have the samelength, e.g., 13 or 14 bits, but for the TIM stations (or non-TIMstations), a specified number of most significant bits shall be set asall 1 or 0 (the specified number could be pre-defined or configuredduring communication or broadcast to the BSS via messages, e.g., abeacon), and the same position of non-TIM stations respectively (or TIMstations respectively) AIDs cannot be set as all 1 or 0 respectively,while the other bits are used for AID assignment. As another example,the AID is 14 bytes in length, and the most significant 7 bits of TIMstations' AIDs are set to all 1 or 0, and the other bits can be used forAID assignment, so the TIM stations AID has the form as shown FIG. 4 andFIG. 5 illustrates a non-TIM station's AID.

The AP may broadcast the information regarding the number of mostsignificant bits set to all 1 or 0 via a beacon. For the indicators inthe TIM, the AP may use the 2̂7 values (the 7 remaining bits of out the14 bit long AID) to represent the TIM stations, and each bit in the TIMindicating the corresponding AID assigned by the 7 remaining bits.

With more than two types of stations, a combination of soft separationand fixed separation may be possible. As an example, fixed separationmay be used to specify AIDs for a first and a second type of station,while soft separation may be used for a third and a fourth type ofstation.

Although in some implementations, such as IEEE 802.11ah, a single AP maysupport a large number of stations, it is expected that an actual numberof TIM stations, such as traffic offloading devices, in thecommunications system to be relatively small due to capacity limits inthe communications system. According to an example embodiment, the TIMmay be generated adaptively to reflect the stations that will actuallybe receiving transmissions. It may be advantageous for the AP toindicate only the stations that will be receiving a transmission fromthe AP instead of transmitting the TIM bitmap which includes indicationsfor every station in the AID address space. Indicating only the stationsthat have downlink data may reduce the length of the TIM, therebyreducing signaling overhead and increasing overall communications systemefficiency.

As an example, the compressed representation of the TIM may be generatedadaptively using a compression TIM generating rule that is known by boththe AP and the stations. The TIM generating rule may specify a format ofa TIM. As an example, the TIM generating rule may specify fields in theTIM, size of the fields, representation of information in the fields,and the like. The TIM generating rule may be used by the AP to generatethe compressed representation of the TIM and the same TIM generatingrule or a corresponding TIM decomposition rule may be used by stationsto extract information from the compressed representation of the TIM.The AP may signal to the stations which TIM generation rule that it isusing to generate the TIM. As an example, the AP may signal the TIMgeneration rule to a station when the station associates with the AP. Asanother example, the AP may signal the TIM generation rule that it willuse to generate a TIM for a subsequent transmission opportunity when itis broadcasting a TIM for a current transmission opportunity. As anotherexample, the AP may signal the TIM generation rule periodically, atspecified time instances, occurrence of an event (an addition of a newstation, a removal of an old station, and the like) or upon receipt ofan instruction. It is noted that the AP may signal an indication of theTIM generation rule, e.g., an index to a list of TIM generation rules,which may represent the TIM generation rule rather than signal theactual TIM generation rule.

FIG. 6a illustrates a TIM 600 that indicates stations receiving atransmission by an AP, TIM 600 is generated according to a firstcompressed TIM generation rule. According to an example embodiment, thefirst TIM generating rule utilizes offsets between a reference AID (e.g.AID=0 corresponding to bit position zero) in the uncompressed TIM bitmapand the AID bit position in the uncompressed TIM bitmap of stationsreceiving transmissions. Practically, the offset represents the distanceexpressed as a number of bits in the uncompressed TIM bitmap between thereference AID and the bit corresponding to the AID of the station thathas data available at the AP. Each offset is referenced to the referenceAID. TIM 600 may include an offset length field 605 that indicates anumber of bits used to represent an offset from a reference AID to anAID of a station that is to receive a transmission from an AP. As anexample, if an offset is a decimal 126, then the offset length must beat least 7 bits long to represent the decimal 126. While, if an offsetis a decimal 65, then the offset length must be at least 7 bits long torepresent the decimal 65. In addition to offset length field 605, TIM600 may include a number of entries field 607 that indicates a number ofentries (e.g., a number of stations receiving transmissions) in TIM 600.TIM 600 may then include a specified number of entries (as specified innumber of entries field 607). As an example, TIM 600 includes N entries,such as entry 1 609, entry 2 611, and entry N 613. A general expressionfor the length of a TIM generated with the first TIM generating rule isexpressible as:

bits=N[log₂(K)]+[log₂(N)]+log₂(MaxTIMbitmap length),

where K is the offset length, and N is the number of entries and [•]operation denotes rounding up to the next integer.

As an illustrative example, consider the following configuration:

-   -   Offset length field 605: 4 bits, capable of representing a        maximum offset length of 13 bits;    -   Number of entries field 607: 13 bits, capable of representing        2¹³ stations;

For discussion purposes, let there be 512 registered stations that needto utilize the TIM. Therefore, a TIM bitmap is 512 bits long. Out of the512 registered stations, only 20 will be receiving a transmission fromthe AP. Therefore, the offset length will be 9 bits (9 bits are requiredto represent 512 values), i.e., offset length field 605 will be 1001.Furthermore, number of entries field 607 will be 00000010100 (binary for20). Each entry (e.g., entry 1 609, entry 2 611, and the like) will be 9bits, therefore, all 20 entries will require 180 bits. Hence, a TIMgenerated according to the first TIM generating rule will be (4+12+180)bits=196 bits (compared to 512 bits for a TIM bitmap).

It is noted that additional savings may be achieved if the entries areencoded in a variable number of bits. FIG. 6b illustrates a TIM 620 thatindicates stations receiving a transmission by an AP, TIM 620 isgenerated according to a modification of the first TIM generation rule.Comparing TIM 620 to TIM 600, an additional field is added. A length ofnumber of entries field 625 is added to support a different field sizefor the number of entries field. Utilizing the same conditions aspresented for the above illustrative example and 4 bits for length ofnumber of entries field 625, a TIM generated according to the modifiedfirst TIM generation rule will be (4+4+5+180)=194 bits.

FIG. 6c illustrates a TIM 640 that indicates stations receiving atransmission by an AP, TIM 640 is generated according to a second TIMgeneration rule. According to an example embodiment, the second TIMgenerating rule utilizes differences between consecutive AIDs ofstations receiving transmissions. TIM 640 may include an offset lengthfield 645 that indicates a number of bits used to represent an offsetfrom a reference AID to an AID of a first station that is to receive atransmission from an AP. As an example, if an offset is a decimal 126,then the offset length must be at least 7 bits long to represent thedecimal 126. While, if an offset is a decimal 65, then the offset lengthmust be at least 7 bits long to represent the decimal 65. In addition tooffset length field 645, TIM 640 may include a number of entries field647 that indicates a number of entries (e.g., a number of stations inaddition to the first station receiving transmissions) in TIM 640.Hence, if there are a total of 5 stations receiving transmissions, thenumber of entries will be 4.

TIM 640 may also include an increment size field 649 that indicates anumber of bits used to represent an increment between AIDs of adjacentstations receiving transmissions. In other words, instead ofrepresenting the offsets with respect to a fixed AID position (i.e., thereference AID) in the uncompressed TIM bitmap, the increments representthe distance in bits between consecutive AID entries of stations withdata in the uncompressed TIM bitmap. As an example, if a maximumdifference between AIDs of adjacent stations is 12, then a smallestincrement that is capable of representing 12 is 4 bits, so incrementsize field 649 may indicate 4 bits for the increment size, while if amaximum difference between AIDs of adjacent stations is 34, then asmallest increment that is capable of representing 34 is 6 bits, soincrement size field 649 may indicate 6 bits for the increment size. TIM640 may also include an offset field 651 that includes an offset from areference AID to an AID of the first station that is to receive atransmission from the AP. TIM 640 may also include a specified number ofentries (as specified in number of entries field 647). As an example,TIM 640 includes N entries, such as entry 1 653, entry 2 655, and entryN 657. As an illustrative example, consider the following situation:Number of stations=512, AIDs of stations receiving transmissions: 300,332, 364, 380, and 384. The offset length is then 9 bits (to representthe offset of 300), hence offset length field requires 4 bits.Therefore, the maximum increment is 32, thereby requiring at least 5bits (however, 8 bits are used in this illustrative example). N is equalto 4, therefore at least 2 bits are required (however, 4 bits are usedin this illustrative example). The entries are: 32, 32, 16, and 4, whichrequire at least 5 bits to represent or a total of 20 bits for all fourentries. Hence, the total number of bits for a TIM generated accordingto the second TIM generating rule is (4+4+8+9+20)=45 bits.

FIG. 6d illustrates a TIM 660 that indicates stations receiving atransmission by an AP, TIM 660 is generated according to a third TIMgeneration rule. According to an example embodiment, the thirdgenerating rule utilizes a mixed format that lends itself to situationswith clustered AIDs. The third TIM generating rule utilizes offsetsbetween a reference AID (e.g., AID 0) and an initial AID of a cluster ofstations and then includes a TIM bitmap of the stations in the cluster.Each offset is referenced to the reference AID. TIM 660 may include anoffset length field 665 that indicates a number of bits used torepresent an offset from a reference AID to an AID of an initial stationof a cluster of stations that is to receive a transmission from an AP.In addition to offset length field 665, TIM 660 may include a number ofentries field 667 that indicates a number of entries (e.g., a number ofclusters of stations receiving transmissions) in TIM 660. Additionally,TIM 660 may include a bitmap size field 669 that indicates a length of abitmap, which corresponds to a number of stations in a cluster. TIM 660may then include a specified number of entries (as specified in numberof entries field 667). As an example, TIM 660 includes N entries, suchas entry 1 671 followed by bitmap 1 673, and entry N 675 followed bybitmap N 677 As an illustrative example, consider the followingsituations: Number of stations=512, AIDs of stations receivingtransmissions: 34, 40, 41, 42, 43, 300, 303, 304, 308, and 315. Offsetlength is then 9 bits (encoded into 4 bits), while the length of entriesis encoded into 4 bits and number of entries is represented using 3bits. Additionally, the bitmap size is represented by 6 bits (i.e.,bitmaps are less than 64 bits long). Then, offset 1=34 and bitmap1=1000001111000000, and offset 2=300 and bitmap 2=1001100010000001.Hence, the total number of bits for a TIM generated according to thethird TIM generating rule is (4+4+3+6+2(9+16)=65 bits.

It is noted that the third TIM generating rule, which makes use ofoffsets between a reference AID and an initial AID of a cluster ofstations may be readily modified to utilize increments between adjacentclusters of stations in a manner similar to the second TIM generatingrule.

FIG. 7a illustrates a flow diagram of operations 700 in an AP as the APtransmits to stations. Operations 700 may be indicative of operationsoccurring in an AP, such as AP 255, as the AP transmits to stations,wherein the AP utilizes a TIM generated according to a TIM generatingrule.

Operations 700 may begin with the AP identifying stations that it istransmitting to (block 705). In general, the AP may be serving a numberof stations, however, in any given transmission opportunity, such as aTTI, the AP may only transmit to a subset of the stations that it isserving. Instead of transmitting to all of the served stations, the APmay transmit to only a subset due to a number of factors, including: theAP may only have data to transmit to some of the served stations, the APmay select the subset of stations according to a selection criteria,such as fairness, priority, quality of service requirements, servicehistory, subscriber level, and the like, network utilization, networkload, availability of data, and the like. As an example, the AP maydetermine the AIDs of the stations.

The AP may generate a TIM according to the stations identified asstations that the AP is transmitting to and a TIM generating rule (block710). As an example, the AP may use the AIDs of the stations inconjunction with the TIM generating rule, e.g., one of the TIMgenerating rules described herein, to generate a TIM. The AP maybroadcast the TIM in a beacon that may be heard by the stations servedby the AP (block 715). It is noted that although the AP is broadcastingthe TIM (in the beacon) to all of its served stations, some of thestations served by the AP, e.g., the non-TIM stations, may ignore someor part of the beacon. The AP may transmit to the stations that itidentified in block 705 (block 720).

FIG. 7b illustrates a flow diagram of operations 750 in a station as thestation receives a transmission from an AP. Operations 750 may beindicative of operations occurring in a station, such as offload device265 and offload device 267, as the station receives a transmission froman AP.

Operations 750 may begin with the station receiving a TIM broadcast in abeacon by the AP (block 755). The station may decode the TIM inaccordance with a TIM generating rule as specified by the AP (block760). The AP may have informed the station of the TIM generating rulethat it is using to generate the TIM when the station associated withthe AP. The AP may have alternatively informed the station of the TIMgenerating rule in a transmission, such as in a previously broadcastbeacon or message.

With the TIM decoded, the station may determine if it is one of thestations indicated in the TIM as receiving a transmission from the AP(block 765). If the station is to receive a transmission from the AP(block 770), then the station will receive a transmission from the AP(block 775). If the station is not to receive a transmission from the AP(block 770), then the station may resume its normal operations or gointo a sleep or suspend mode.

FIG. 8a illustrates a first beacon 800 for supporting multiple stationtypes. According to an example embodiment, in order to support multiplestation types, a beacon may include a separate common data area and aseparate TIM area. Furthermore, the common data area and the TIM areashould be encoded separately so that a station that is not interested inthe TIM area does not need to detect and decode the TIM area in order todetect and decode the common area. First beacon 800 includes a signal(SIG) physical layer (PHY) preamble 805 that may include a beaconindicator 807, which may be a one or more bit indicator indicating thata beacon is being transmitted. SIG PHY preamble 805 may also include adata duration field 809 that indicates a duration (e.g., in time orsymbols) of a common data area of first beacon 800 and a TIM durationfield 811 that indicates a duration (e.g., in time or symbols) of a TIMarea of first beacon 800.

First beacon 800 also includes a common data area comprising a commondata field 813 and a cyclic redundancy check (CRC) field 815 for commondata field 813, and a TIM area comprising a TIM bitmap 817 and a CRCfield 819 for TIM bitmap 817. As discussed above, the duration of commondata field 813 may be specified by data duration field 809, while TIMduration field 811 may specify the duration of TIM bitmap 817.Additionally, common data field 813 and TIM bitmap 817 may be separatelyencoded so that a station that is not interested in the TIM bitmap maynot need to detect and decode TIM bitmap 817 in order to detect anddecode common data field 813.

FIG. 8b illustrates a second beacon 830 for supporting multiple stationtypes. Second beacon 830 includes a SIG PHY preamble 835 that mayinclude a beacon indicator 837 to indicate that a beacon is beingtransmitted, and a separate encoded block indicator 839 to indicate thatsecond beacon 830 includes more than one block of separately encodedinformation. It is noted that beacon indicator 837 may be used in placeof separate encoded block indicator 839 meaning that beacon indicator837 may indicate both a beacon being transmitted and that the beaconincludes more than one block of separately encoded information. SIG PHYpreamble 835 may also include a data duration field 841 that indicates aduration (e.g., in time or symbols) of a common data area of secondbeacon 830 and a TIM duration field 843 that indicates a duration (e.g.,in time or symbols) of a TIM area of second beacon 830.

Second beacon 830 also includes a common data area comprising a commondata field 845 and a CRC field 847 for common data field 845, and a TIMarea comprising a TIM bitmap 849 and a CRC field 851 for TIM bitmap 849.As discussed above, the duration of common data field 845 may bespecified by data duration field 841, while TIM duration field 843 mayspecify the duration of TIM bitmap 849. Additionally, common data field845 and TIM bitmap 849 may be separately encoded so that a station thatis not interested in the TIM bitmap may not need to detect and decodeTIM bitmap 849 in order to detect and decode common data field 845.

FIG. 8c illustrates a third beacon 860 for supporting multiple stationtypes. Third beacon 860 includes a SIG PHY preamble 865 that may includea beacon indicator 867 to indicate that a beacon is being transmitted.SIG PHY preamble 865 may also include a data duration field 869 thatindicates a duration (e.g., in time or symbols) of a common data area ofthird beacon 860.

Third beacon 860 also includes a common data area 871 comprising a TIMduration field 873 that indicates a duration (e.g., in time or symbols)of a TIM area of third beacon 860. Common data area 871 also includes anadditional data field 875 and a CRC field 877 for common data field 871,and a TIM area comprising a TIM bitmap 879 and a CRC field 881 for TIMbitmap 879. With third beacon 860, non-TIM stations may detect anddecode just common data area 871 using data duration field 869, whileTIM stations may detect and decode the TIM area using TIM duration field873 in common data area 871.

According to an alternative example embodiment, a beacon may not includea TIM area. The beacon may just include a common data area and acorresponding TIM area may be transmitted in a separate message, whichmay be another beacon or a non-beacon transmission. The correspondingTIM area may or may not be periodic in nature and may be transmittedadaptively based on traffic, e.g., downlink traffic, patterns orprovided upon request from a station(s).

As discussed above, the duration of common data field 845 may bespecified by data duration field 841, while TIM duration field 843 mayspecify the duration of TIM bitmap 849. Additionally, common data field845 and TIM bitmap 849 may be separately encoded so that a station thatis not interested in the TIM bitmap may not need to detect and decodeTIM bitmap 849 in order to detect and decode common data field 845.

FIG. 9a illustrates a flow diagram of operations 900 in an AP generatinga beacon. Operations 900 may be indicative of operations occurring in anAP, such as AP 255, generates a beacon. The beacon generated by the APincludes support for TIM and non-TIM station operation.

Operations 900 may begin with the AP generating a SIG PHY preamble forthe beacon (block 905). The SIG PHY preamble may include a beaconindicator and/or a separate encoded block indicator. The SIG PHYpreamble may also include data duration information. Depending on thebeacon, the SIG PHY preamble may further include TIM durationinformation.

The AP may generate and encode information to be included in the commondata portion of the preamble, which may be detected and decoded by bothTIM and non-TIM stations (block 907). If the common data portion of thepreamble also includes TIM duration information, the AP may place suchinformation in the common data portion. The AP may generate a CRC forthe common data portion of the preamble. The AP may generate and encodeinformation to be included in the TIM portion of the preamble, which maybe detected and decoded by TIM stations (block 909). The AP may generatea CRC for the TIM portion of the preamble. The AP may transmit thepreamble.

FIG. 9b illustrates a flow diagram of operations 930 in a TIM stationreceiving a beacon. Operations 930 may be indicative of operationsoccurring in a TIM station, such as an offload device 265 and offloaddevice 267, as the TIM station receives a beacon.

Operations 930 may begin with the TIM station detecting a SIG PHYpreamble of the beacon (block 935). The SIG PHY preamble may include,depending on beacon configuration: a beacon indicator, a separateencoded block indicator, data duration information, TIM durationinformation, common data, a TIM bitmap, or a combination thereof. TheTIM station may detect and decode the common data part of the beacon(block 937). Since the TIM station needs information in the TIM bitmap,the TIM station may also detect and decode the TIM part of the beacon(block 939).

FIG. 9c illustrates a flow diagram of operations 960 in a non-TIMstation receiving a beacon. Operations 960 may be indicative ofoperations occurring in a non-TIM station, such as sensor 260, andsensor 262, as the non-TIM station receives a beacon.

Operations 960 may begin with the non-TIM station detecting a SIG PHYpreamble of the beacon (block 965). The SIG PHY preamble may include,depending on beacon configuration: a beacon indicator, a separateencoded block indicator, data duration information, TIM durationinformation, common data, a TIM bitmap, or a combination thereof. Thenon-TIM station may detect and decode the common data part of the beacon(block 967). However, since the non-TIM station does not generally needinformation in the TIM bitmap, the non-TIM station typically does notdetect and decode the TIM part of the beacon. Although, in some exampleembodiments, the non-TIM station may periodically or occasionally detectand decode the TIM part of the beacon.

FIG. 10 provides an illustration of a first communications device 1000.Communications device 1000 may be an implementation of a communicationscontroller, such as an access point, a base station, an evolved NodeB,and the like. Communications device 1000 may be used to implementvarious ones of the embodiments discussed herein. As shown in FIG. 10, atransmitter 1005 is configured to send packets and/or signals and areceiver 1010 is configured to receive packets and/or signals.Transmitter 1005 and receiver 1010 may have a wireless interface, awireline interface, or a combination thereof.

A beacon generating unit 1020 is configured to generate a beacon for useby TIM and non-TIM stations. Beacon generating unit 1020 is alsoconfigured to generate a TIM according to a TIM generating rule andstations that communications device 1000 is transmitting to. The beaconmay include: a SIG PHY preamble, a common data portion, a TIM portion,or a combination thereof. The beacon may include indicators, durationinformation, block encoding information, or a combination thereof. Anidentifying unit 1022 is configured to identify stations thatcommunications device 1000 is transmitting to. Identifying unit 1022 isconfigured to identify stations according to a selection criteria, suchas fairness, priority, quality of service requirements, service history,subscriber level, and the like, network utilization, network load,availability of data, and the like. A buffering unit 1024 is configuredto buffer data, such as downlink data and/or uplink data, received bycommunications device 1000. A memory 1030 is configured to storebeacons, duration information, indicators, CRC, common data, TIMinformation, TIM bitmaps, data, identified stations, and so on.

The elements of communications device 1000 may be implemented asspecific hardware logic blocks. In an alternative, the elements ofcommunications device 1000 may be implemented as software executing in aprocessor, controller, application specific integrated circuit, or soon. In yet another alternative, the elements of communications device1000 may be implemented as a combination of software and/or hardware.

As an example, transmitter 1005 and receiver 1010 may be implemented asa specific hardware block, while beacon generating unit 1020,identifying unit 1022, and buffering unit 1024 may be software modulesexecuting in a processor 1015, a microprocessor, a custom circuit, or acustom compiled logic array of a field programmable logic array. Beacongenerating unit 1020, identifying unit 1022, and buffering unit 1024 maybe stored as modules in memory 1030.

FIG. 11 provides an illustration of a second communications device 1100.Communications device 1100 may be an implementation of a communicationsdevice, such as a station, a sensor, an offload device, a userequipment, and the like. Communications device 1100 may be used toimplement various ones of the embodiments discussed herein. As shown inFIG. 11, a transmitter 1105 is configured to send packets and/or signalsand a receiver 1110 is configured to receive packets and/or signals.Transmitter 1105 and receiver 1110 may have a wireless interface, awireline interface, or a combination thereof.

A request processing unit 1120 is configured to generate a request fordata, such as downlink data and/or uplink data, from a communicationscontroller. The request for the data may be an explicit request or animplicit request. A detecting/decoding unit 1122 is configured to detectand/or decode transmissions. As an example, detecting/decoding unit 1122detects and decodes a common data portion of a beacon, a TIM portion ofthe beacon, or both. A beacon processing unit 1124 is configured toprocess information included in the beacon, such as decoding a TIM. Asan example, beacon processing unit 1124 processes the beacon todetermine a duration of the common data portion, to determine if thecommon data portion and the TIM portion are separately encoded, and thelike. Beacon processing unit 1124 utilizes a TIM generating rule asspecified by an AP to decode a TIM. A memory 1130 is configured to storebeacons, duration information, indicators, CRC, common data, TIMinformation, TIM bitmaps, and so on.

The elements of communications device 1100 may be implemented asspecific hardware logic blocks. In an alternative, the elements ofcommunications device 1100 may be implemented as software executing in aprocessor, controller, application specific integrated circuit, or soon. In yet another alternative, the elements of communications device1100 may be implemented as a combination of software and/or hardware.

As an example, transmitter 1105 and receiver 1110 may be implemented asa specific hardware block, while request processing unit 1120,detecting/decoding unit 1122, and beacon processing unit 1124 may besoftware modules executing in a processor 1115, a microprocessor, acustom circuit, or a custom compiled logic array of a field programmablelogic array. Request processing unit 1120, detecting/decoding unit 1122,and beacon processing unit 1124 may be stored as modules in memory 1130.

Although the present disclosure and its advantages have been describedin detail, it should be understood that various changes, substitutionsand alterations can be made herein without departing from the spirit andscope of the disclosure as defined by the appended claims.

What is claimed is:
 1. A method for operating a station having anindicator indicating whether the station supports a traffic indicationmap (TIM), the method comprising: receiving, by the station from anaccess point (AP), a downlink unicast beacon comprising TIM informationand common data information; detecting, by the station, a sub 1 GHz(SIG) physical layer (PHY) preamble of the downlink unicast beacon; andignoring, by station, the TIM information in the downlink unicast beaconif the indicator indicates that the station does not support the TIM. 2.The method of claim 1, further comprising: detecting and decoding, bythe station, the common data information in the downlink unicast beacon.3. The method of claim 1, wherein the indicator is a portion of anaccess identifier (AID), wherein the indicator set to 1 indicates thatthe station does not support the TIM, and wherein the indicator set to 0indicates that the station supports the TIM.
 4. The method of claim 1,wherein the station is in a power save mode if the indicator indicatesthat the station does not support the TIM.
 5. The method of claim 4,wherein the station wakes up after the power save mode and the indicatoris reset to indicate that the station supports the TIM.
 6. The method ofclaim 5, further comprising: detecting the TIM information in thedownlink unicast beacon after the station is waked up after the powersaved mode.
 7. The method of claim 1, wherein the indicator is anaddress indictor.
 8. A method for operating an access point (AP), themethod comprising: receiving, by the access point, information from aplurality of stations, wherein a first station of the plurality ofstations is operating in a non-traffic-indication-map (non-TIM) mode;generating, by the AP, a downlink unicast beacon comprising a sub 1 GHz(SIG) physical layer (PHY) preamble, traffic-indication-map (TIM)information and common data information, wherein the TIM information isgenerated in accordance with a TIM generating format, and wherein theTIM information is ignored by the first station operating in the non-TIMmode; and transmitting, by the AP, the downlink unicast beacon to theplurality of stations.
 9. The method of claim 8, further comprising:waking up the first station operating in the non-TIM mode; and settingan access identifier (AID) of the first station to indicate that thefirst station is to operate in a TIM mode.
 10. The method of claim 9,wherein a portion of the AID is an indicator, wherein the indicator setto 1 indicates that the station does not support the TIM, and whereinthe indicator set to 0 indicates that the station supports the TIM. 11.A station having an indicator indicating whether the station supports atraffic indication map (TIM), the station comprising: a receiverconfigured to receive, from an access point (AP), a downlink unicastbeacon comprising TIM information and common data information; and aprocessor operatively coupled to the receiver and configured to: detecta sub 1 GHz (SIG) physical layer (PHY) preamble of the downlink unicastbeacon; and ignore the TIM information in the downlink unicast beacon ifthe indicator indicates that the station does not support the TIM. 12.The station of claim 11, wherein the processor is further configured to:detect and decode the common data information in the downlink unicastbeacon.
 13. The station of claim 11, wherein the indicator is a portionof an access identifier (AID), wherein the indicator set to 1 indicatesthat the station does not support the TIM, and wherein the indicator setto 0 indicates that the station supports the TIM.
 14. The station ofclaim 11, wherein the station is in a power save mode if the indicatorindicates that the station does not support the TIM.
 15. The station ofclaim 14, wherein the station wakes up after the power save mode and theindicator is reset to indicate that the station supports the TIM. 16.The station of claim 15, wherein the processor is further configured to:detect the TIM information in the downlink unicast beacon after thestation is waked up after the power saved mode.
 17. The station of claim11, wherein the indicator is an address indictor.
 18. An access point(AP) comprising: a receiver configured to receive information from aplurality of stations, wherein a first station of the plurality ofstations is operating in a non-traffic-indication-map (non-TIM) mode; aprocessor operatively coupled to the receiver and configured to generatea downlink unicast beacon comprising a sub 1 GHz (SIG) physical layer(PHY) preamble, traffic-indication-map (TIM) information and common datainformation, wherein the TIM information is generated in accordance witha TIM generating format, and wherein the TIM information is ignored bythe first station operating in the non-TIM mode; and a transmitteroperatively coupled to the processor and configured to transmit thedownlink unicast beacon to the plurality of stations.
 19. The AP ofclaim 18, wherein the processor is further configured to: wake up thefirst station operating in the non-TIM mode; and set an accessidentifier (AID) of the first station to indicate that the first stationis to operate in a TIM mode.
 20. The AP of claim 19, wherein a portionof the AID is an indicator, wherein the indicator set to 1 indicatesthat the station does not support the TIM, and wherein the indicator setto 0 indicates that the station supports the TIM.